> For the complete documentation index, see [llms.txt](https://docs.mapbox.com/mapbox-gl-js/ja/llms.txt)
# Create a hover effect
Use events and [feature states](https://docs.mapbox.com/mapbox-gl-js/ja/api/map/#map#setfeaturestate) to create a per feature hover effect.
To add a tooltip that follows the mouse to complement the hover effect, see the [Add a hover tooltip that follows the mouse pointer](https://docs.mapbox.com/mapbox-gl-js/ja/example/hover-tooltip/) example.
> Example code:
**JavaScript**
```html
Create a hover effect
```
**React**
```jsx
import React, { useEffect, useRef } from 'react';
import * as mapboxgl from 'mapbox-gl/esm';
import 'mapbox-gl/dist/mapbox-gl.css';
const MapboxExample = () => {
const mapContainerRef = useRef();
const mapRef = useRef();
useEffect(() => {
mapRef.current = new mapboxgl.Map({
// TO MAKE THE MAP APPEAR YOU MUST
// ADD YOUR ACCESS TOKEN FROM
// https://account.mapbox.com
accessToken: 'YOUR_MAPBOX_ACCESS_TOKEN',
container: mapContainerRef.current,
// Choose from Mapbox's core styles, or make your own style with Mapbox Studio
style: 'mapbox://styles/mapbox/standard',
center: [-100.486052, 37.830348],
zoom: 2
});
let hoveredPolygonId = null;
mapRef.current.on('load', () => {
mapRef.current.addSource('states', {
type: 'geojson',
data: 'https://docs.mapbox.com/mapbox-gl-js/assets/us_states.geojson'
});
// The feature-state dependent fill-opacity expression will render the hover effect
// when a feature's hover state is set to true.
mapRef.current.addLayer({
id: 'state-fills',
type: 'fill',
source: 'states',
layout: {},
paint: {
'fill-color': '#627BC1',
'fill-opacity': [
'case',
['boolean', ['feature-state', 'hover'], false],
1,
0.5
]
}
});
mapRef.current.addLayer({
id: 'state-borders',
type: 'line',
source: 'states',
layout: {},
paint: {
'line-color': '#627BC1',
'line-width': 2
}
});
mapRef.current.on('mousemove', 'state-fills', (e) => {
if (e.features.length > 0) {
if (hoveredPolygonId !== null) {
mapRef.current.setFeatureState(
{ source: 'states', id: hoveredPolygonId },
{ hover: false }
);
}
hoveredPolygonId = e.features[0].id;
mapRef.current.setFeatureState(
{ source: 'states', id: hoveredPolygonId },
{ hover: true }
);
}
});
mapRef.current.on('mouseleave', 'state-fills', () => {
if (hoveredPolygonId !== null) {
mapRef.current.setFeatureState(
{ source: 'states', id: hoveredPolygonId },
{ hover: false }
);
}
hoveredPolygonId = null;
});
});
}, []);
return ;
};
export default MapboxExample;
```